


oh, your mask is slipping

by avosettas



Category: Undertale (Video Game)
Genre: Dreamtale Nightmare Sans (Undertale), Ecto-Breasts (Undertale), Ecto-Genitalia (Undertale), Ecto-Penis (Undertale), Ecto-Vagina (Undertale), Empath Nightmare, Errortale Sans (Undertale), Errortale Sans/Dreamtale Nightmare Sans (Undertale), M/M, Nipple Play, Self Confidence Issues, haha ao3 tags go brrrr
Language: English
Status: Completed
Published: 2021-02-13
Updated: 2021-02-13
Packaged: 2021-03-12 19:41:54
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,245
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/29390001
Author URL: https://archiveofourown.org/users/avosettas/pseuds/avosettas
Summary: “D-do you r-really think-k-k-k-k -” There’s a clicking sound as Error crashes, though he’s back up so quickly that Nightmare barely registers theREBOOTINGbar above his head. “Who th-thefuckl-laughed a-at you?!”“No one who’s still alive,” Nightmare assures him bitterly.
Relationships: Sans/Sans (Undertale)
Comments: 3
Kudos: 132





	oh, your mask is slipping

**Author's Note:**

> for neah!
> 
> my brain did NOT want to work on this - 5 hours of work on it today, and that was barely half of it.   
> hence why i'm blanking on tags

“W-would you… form wh-what you’re actually _comfortable_ with, for once?” 

The fact that Error had asked to be in control this time was odd enough, but it was this second request that Nightmare was confusing Nightmare. More so than that, it was the fact that he was apparently perceptive enough to see beyond Nightmare’s layers of calculated, controlled calmness. Even Killer couldn’t manage that most days, and he’d known Nightmare longer than anyone, save for Dream.

“Are you going to stare at me, if I do this?” Compared to Error’s snappish tone, it’s embarrassing how resigned Nightmare sounds; even his tentacles are hanging limp behind him, defeated. Usually they’d snark at each other until kingdom come; now, he’s trying to resist the urge to curl in on himself, while Error stares, scowling with confusion. 

“Why w-wouldn’t I stare at you?” Error replies, cocking his head. “I l-like the way you look.” 

“That isn’t what I meant -” 

“I’m not gonna _laugh_ a-at you, or something awful like that,” Error interrupts, and the anger that radiates from him makes Nightmare feel better, even as he prods at it from beneath the layers of confusion and dismay. 

“You might.” He’s never made it a secret that he’s not fond of his body. Of course, he’s never been all that obvious about the hatred he has for his own form, either; instead, he forces himself to radiate a condescending air, lest someone think him pitiful, or even worse, _weak_.

At least the changes he underwent from eating the apples made it easier to distance himself from the past. Though of course, much of that had little to do with his ecto-body. Much of it had to do with simply who he was, down to his rotten apple core. 

“D-do you r-really think-k-k-k-k -” There’s a clicking sound as Error crashes, though he’s back up so quickly that Nightmare barely registers the **REBOOTING** bar above his head. He’s even angrier now, and Nightmare takes it in, trying to forget that he’s probably the cause of it. 

He nearly misses Error’s next words, still choppy from his sudden reboot, and he almost completely misses the slight rewording. “Who th-the _fuck_ l-laughed a-at you?!”

“No one who’s still alive,” Nightmare assures him bitterly. Error snorts a bit in response, his posture relaxing slightly as he returns back to his usual slouched position. 

“Good. Th-they’d be dead by m-my hands now, anyway,” he says darkly. Then, he sighs, deflating even more, but Nightmare can only feel resignation from him. Before he can ask, Error looks at him again, and continues, “I w-want you to be comfortable with what y-you form, but I also want you t-to be comfortable with your body i-in general.” 

“Both of those are tall orders,” Nightmare tells him. “But I can try.” 

The surprise is clear not only on Error’s face, but in the emotions that radiate from him, and below that, Nightmare can feel something positive - Error’s pleased, he thinks. It’s not an emotion that empowers Nightmare, but he enjoys it all the same, since it’s coming from Error. 

He mumbles something that Nightmare can’t quite make out, though based on the faint gratefulness that he can feel, it was probably an expression of thanks. Then, he presses his teeth to Nightmare’s, so gentle that it’s almost surprising. 

When Error leans back, he’s already slightly flushed with an array of the primary colors, looking rather like a watercolor painting. Nightmare has always found that to be his favorite part of any intimacy with Error - getting to see him flushing all red and blue and yellow is a treat all of its own. He can barely resist leaning in to kiss Error again, though he manages it. 

“Can I touch?” he asks instead. Error snorts a bit, and kisses him again, deeper this time. 

Nightmare has never gotten used to the sensation of Error’s five tongues against his own, though he’s one to talk; it’s unlikely Error’s become used to the sensation of liquid negativity against his bones, even after all this time. The difference is that Nightmare finds Error’s tongues to be pleasant - he can’t imagine any universe where the slime covering his own body would be. 

It’s a pleasant sort of strange, though, especially when Error decides to settle his hands on Nightmare’s iliac crests. His fingers find their way between Nightmare’s waistband and the hem of his sweater, letting his thumbs rest on what passes for bare bone. They rub soft circles into the oozing negativity there; the substance is only slightly more malleable than actual bones. 

Certainly, it isn’t enough to actually get him aroused - at least, not this early - but it’s pleasant and relaxing enough that Nightmare finds himself slumping slightly into Error’s hold, dropping his skull onto his partner’s shoulder when they break the kiss. He hears Error laugh a little; one of his tentacles has decided to make itself at home, curling around Error’s waist. 

Error’s hands find their way to Nightmare’s ribcage, slowly tracing between the intercostal spaces through his sweater as if he has all the time in the world. Nightmare, for his part, simply keeps his head on Error’s shoulder, turning to face the crook of his neck. He knows he’ll be embarrassed whenever his magic decides to show itself, so he might as well preempt his instinct to hide. 

“You o-okay?” Error asks, and his voice is a soothing sort of crackling, right besides Nightmare’s head. One hand moves beneath his sweater, resting on his sternum as its owner waits for his answer. 

So Nightmare nods, trying to ignore the budding anxiousness that comes with the feeling of his magic coalescing beneath his ribcage and in his pelvis. He wishes that he wasn’t so goddamn sensitive; even Error’s soft caresses to his sternum have his ecto-body itching to form.

It must be noticeable, because Error lets his hands fall to Nightmare’s floating ribs as he murmurs, “I-it’s alright, you can let y-your magic go…” 

Nightmare scrunches his eye shut and presses his face further into Error’s bulky hoodie, letting go of his hold on the persistent magic. Error moves one of his thumbs slightly, gently stroking down the length of the floating rib it rests on, and that’s all it takes. 

Nightmare gasps, perhaps a little wetly, when his magic brings itself together into a coherent body. Error’s touch is grounding; he doesn’t move his hands, except when Nightmare’s magic pushes them from his ribs to the newly-formed pseudo-flesh that covers them. 

He doesn’t want to know what Error’s expression looks like, and though it takes effort, he focuses on blocking out the other’s emotional responses as best he can. 

“Nightmare,” Error’s voice says through his self-loathing. He’s pulled Nightmare to his chest, holding his skull gently to his shoulder. Slowly, Nightmare registers that his tentacles have wrapped around Error as well, an automatic and embarrassing comfort response. 

“Sorry,” Nightmare says, muffled. He forces his tentacles to release Error, letting them fall into semicircles around his partner on the bed. “I’m fine.” 

As he says it, he lets Error’s emotions hit him again - he’s annoyed, and beyond that is a mess of positive emotions that Nightmare couldn’t decipher if he tried. It’s odd to realize that they’re connected to _him_ , of all people. 

“D-do you - do y-you need to -” 

Nightmare interrupts with a shake of his head, and finally he leans back from Error’s embrace. Error’s face is still awash with a mix of colors, and try as he might, his eyelights are very obviously flicking downwards every so often. 

“I’m fine,” he repeats, softer but firmer. After a moment, he amends, “Nervous, but fine,” because if he can’t admit that to his partner, who can he admit it to? 

Error stares at him, clearly disbelieving, but his hands return to Nightmare’s waist, resting now on the false flesh of his hips. “Pr-promise?” 

“Promise.” He hates how weak his voice sounds, but Error takes the confirmation despite the fact that it sounds like Nightmare might cry. Once again his hands work their way beneath Nightmare’s sweater, skating up his sides with gentle touches. 

Even despite the care that Error handles him with, and despite how soft and slow each movement is, Nightmare still shivers when his partner reaches his breasts, the tips of Error’s distals pressing softly into his pseudo-flesh. He exhales shakily, reaching for Error’s shoulders. 

Error goes back to his hips, fingers fiddling with the hem of Nightmare’s sweater. When he opens his mouth, Nightmare nods before he can speak, a shaky but affirmative hum accompanying the motion. He can hardly bear to move his hands from where they clutch at Error, and he hates to admit that he misses Error’s hand on his body, but he manages both to allow his sweater to be removed. 

“D-don’t know what you w-were afraid of,” Error murmurs, running his hands up Nightmare’s sides, settling back on his breasts. “I th-think you look great.” 

Nightmare just sighs a bit shakily in response, though it turns to a gasp when Error rubs over his nipples a few times. The very tip of one of his distals presses onto one of the inverted nubs, making Nightmare keen as Error continues trying to tug it out. His other hand is focused on kneading Nightmare’s opposite breast, the pressure firm but pleasant. 

Error kisses him again, and Nightmare moans into it as both hands are focused on his nipples, tugging and twisting at them leisurely. When he breaks their kiss, Nightmare is panting from the stimulation, and already there’s a warm pressure in his center, born of arousal. 

“Error,” he whines, breaking into a groan when Error leans down and laps at his breast, his quintet of tongues practically smothering Nightmare’s nipple. He arches into it, moaning as Error suckles. Error hums as he switches to the other breast, swirling his tongues teasingly. 

“Error, please,” Nightmare begs again, and Error finally leans back slightly, one hand replacing his mouth while the other tugs at Nightmare’s waistband. 

“Didn’t think th-that would get you s-so wound up,” he laughs. He barely tugs Nightmare’s pants down, instead making do with slipping his hand under the waistband. “You’re r-really wet.” 

Nightmare tries to reply with something biting, but Error presses onto his clit, and he keens instead. Error is resting his forehead on Nightmare’s shoulder, now, panting breaths hitting Nightmare’s chest each time he exhales. He turns his head a bit to mouth at Nightmare’s cervical vertebrae, just as the hand he has at Nightmare’s clit slips through his folds to his entrance. 

Error doesn’t press his finger in immediately, instead softly rubbing at Nightmare’s folds, collecting the slick built up between them. He huffs a soft laugh when Nightmare rocks his hips slightly, though he shuts up quickly when the other glares at him. 

“Just fuck me,” Nightmare grunts, releasing Error’s shoulders only to shimmy his pants down. They’re so close together, though, that he only gets them halfway down his thighs before he gives up, throwing his arms back around Error’s shoulders. 

“N-needy,” Error mumbles, resituating his finger and pressing in. Nightmare’s claws dig into his hoodie, hands pressing down onto Error’s shoulders as he rocks himself. He’s practically dripping already, and Error tells him so as he works another finger in. 

“Please,” Nightmare whines in response. Error splays his fingers, pulling a moan from Nightmare, and then pulls them out. 

“You’re i-impatient,” he tells Nightmare, scooting forward as much as he can before pushing Nightmare down into the bed. 

Nightmare’s eyelight is blown out and fuzzy as he watches Error shove his shorts down, just as impatiently as his partner had earlier. Nightmare hooks one leg around his back, drawing him closer clumsily, and Error laughs, a sound that Nightmare loves despite it having the sound of a printer doing its work. 

“R-really impatient,” Error repeats, gripping Nightmare’s hip with his clean hand and guiding his dick with the other. Nightmare rolls his eye slightly, though it closes completely when Error pushes in with one long thrust. 

The pace he sets isn’t quite rhythmic, as every so often he glitches from the pleasure, but Error keeps up a steady stream of mumbled praise. Nightmare can only glean even that from his tone and his emotions; the actual words are too soft to hear, and distorted by Error’s glitches every so often. The meaning is clear, though, and Nightmare lets it wash over him as Error fucks him. 

Error is busy trying to keep himself steady through his glitches, both hands holding Nightmare’s hips as his pace grows more erratic. Whenever his hands glitch, Nightmare’s hips tingle slightly, as if he’s walking on a foot that’s fallen asleep. 

Nightmare reaches down, rubbing fiercely at his clit as Error’s voice is overtaken completely by the glitching, a sign that he’s very close. Somehow, he still cums first, tensing hard before falling limp as Error thrusts a few more times. 

Then, there’s a noise similar to a busy signal, and Nightmare twitches as Error cums inside him, before collapsing, a **REBOOTING** bar above his head. It’s moving slowly, but steadily; even so, Nightmare pulls his partner closer with a sigh. 

He’ll be here when Error wakes up, whenever it’s heralded with that little dial-up noise he’s so familiar with. He’s content to wait. 

He… does kind of wish that Error had managed to pull out before crashing, though.

**Author's Note:**

> twitter @avosettas


End file.
